The present invention relates to digital transmission systems and more particularly to the detecting of errors in such systems.
In digital transmission systems it is common to use redundant coding to aid transmission. A typical form of redundant coding is that known as 4B3T in which 4-digit binary words are re-coded into 3-digit ternary words. The re-coding can be arranged so that the disparity of the transmitted signals can be kept to a minimum. Also, in digital transmission systems it is common to provide error detection facilities such as parity checking. However, such checking requires that parity check information be transmitted in addition to the digital signals which are being checked. One way of doing this is to send extra signals and to allow for these by increasing the digit rate of the system.